1. Field of the Invention
The present invention relates generally to a composite structure comprising a high density of hard metallic particles, such as tungsten carbide, uniformly disposed within a matrix of a softer brazing metal or alloy and to a method of making the same.
2. Prior Art
In order to form a material which combines the excellent wear resistance of hard materials such as metal oxides, silicides, borides and carbides with the ductility of softer metals, composite materials have been devised consisting of the soft material. For example, U.S. Pat. 3,684,497 discloses a class of composite materials which includes tungsten carbide particles disposed in a matrix of a copper alloy. That patent suggests such a composite has utility in heat resistant and drill proof armor plates for safe or vault protection as well as in high wear applications. The hard particles provide the necessary resistance to wear and to penetration while the softer, more thermally conductive matrix provides torch protection and gives the composite material a toughness which substantially exceeds that of the hardened material.
The relative percentages of the hard particles and the soft matrix will vary as a function of the application but in most applications it is desirable that the hard particles predominate and the matrixing material be present in only sufficient quantity to firmly bond the hard particles into the composite. The aforementioned patent discloses one prior art method of achieving this high density of hard particles in the soft matrix involving packing a mold with particles of a relatively large average particle size and a sufficient amount of softer metal, in powder form, to coat the hard particles an bind them into a unitary, porous skeleton, when the mold is placed in a brazing furnace. This skeleton is then coated with a mixture of hard particles of substantially smaller average particle size and further alloy powder and passed through the furnace a second time. The finer particles tend to infiltrate the skeleton of the larger particles with the flow of the molten alloy powder to increase the density of hard particles in the resulting structure. By use of this method I have been able to achieve structures wherein the hard particles represent about 60% by volume of the finished product. In certain wear applications this density has proved inadequate and the relatively high proportion of softer materials has caused surface erosion which severely curtails the life of wear resistant parts formed by this process.